XML documents are made up of storage units called entities, which contain either parsed or unparsed data. Parsed data is made up of characters, some of which form character data and some of which form markup. Markup encodes a description of the document's storage layout and logical structure. XML provides a mechanism to impose constraints on the storage layout and logical structure.

The RDF is a foundation for processing metadata; it provides interoperability between applications that exchange machine-understandable information on the Web. RDF uses XML to exchange descriptions of Web resources but the resources being described can be of any type, including XML and non-XML resources. RDF emphasizes facilities to enable automated processing of Web resources. RDF can be used in a variety of application areas, for example, in resource discovery to provide better search engine capabilities; in cataloging for describing the content and content relationships available at a particular Web site, page, or digital library, by intelligent software agents to facilitate knowledge sharing and exchange; in content rating; in describing collections of pages that represent a single logical document; in describing intellectual property rights of Web pages; and in expressing the privacy preferences of a user as well as the privacy policies of a Web site. RDF with digital signatures is the key to building the Web of Trust for electronic commerce, collaboration, and other applications.

The goal of the CC/PP framework is to specify how client devices express their capabilities and preferences (the user agent profile) to the server that originates content (the origin server). The origin server uses the user agent profile to produce and deliver content appropriate to the client device. In addition to computer-based client devices, particular attention is paid to other kinds of devices such as mobile phones.

The requirements on the framework emphasize three aspects: flexibility, extensibility, and distribution. The framework must be flexible since we cannot today predict all the different types of devices that will be used in the future or the ways those devices will be used. It must be extensible for the same reasons: it should not be hard to add and test new descriptions, and it must be distributed, since relying on a central registry might make it inflexible.

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